Control mechanism for fuel injection apparatus



F. FUCHS 3,409,276

CONTROL MECHANISM FOR FUEL INJECTION APPARATUS Nov. 5', 1968 Filed Jan. 22, 1968 .7"- FUEL FLOW AIR FLOW in 0 5 o .llx (l I I I I I I I I l I I I .ll 6 n 0.- O/lb/ c b ll 7 M T N A w a N m w- 2 a m 1; 1 J m 0 O O O 0. t P

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INVENTOR FRANZ FUCHS ATTORNEYS United States Patent 3,409,276 CONTROL MECHANISM FOR FUEL INJECTION APPARATUS- Franz Fuchs, Pocking, Germany, assignor to Junkers Flugzeugund Motorenwerke G.m.b.H., Munich, Germany Continuation-impart of application Ser. No. 561,933,

June 30, 1966. This application Jan. 22, 1968, Ser- No. 699,447

8 Claims. (Cl. 26150) ABSTRACT OF THE DISCLOSURE A fuel injection apparatus including fuel valve means is controlled jointly by a differential air pressure device and a differential fuel pressure device. The differential air pressure device is supplied with apressure differential derived from an elongated control duct of uniform crosssectional area bypassing a throttle controlled air flow passage. The mixture ratio can be adjusted manually, or as a function of any desired parameter, by means of a control valve associated with the inlet to said control duct.

Cross-reference to related application The instant application comprises a continuation in part of my prior copending application Serial No. 561,- 933 filed June 30, 1966, for-Control Mechanism for Fuel Injection Apparatus, now abandoned. I

Background 0] the invention The present invention relates to fuel supply systems for combustion engines, arranged to meter a quantity of fuel as a function of the quantity of combustion air supplied to the engine. More particularly, the present invention relates to fuel control mechanisms wherein air flow to an engine is measured by subjecting an air-flow diaphragm to a differential air pressure constituting a measure of the air flow to the engine, with said air-flow diaphragm being in turn coupled to, and force balanced against, a fuel-flow diaphragm subjected to a differential fuel pressure indicative of the quantity of fuel being supplied to the engine.

Arrangements of the general type described above have already been suggested for use with low-pressure carburetor systems where the volume of air supplied to the engine is measured and, in response to this measurement, a measured quantity of fuel is injected into the intake duct of the engine. Known apparatuses of thi type characteristically measure the quantity of air flow by monitoring the pressure differential across a stationary venturi (as in US. Patent No. 2,295,656), or by employing several consecutive movably arranged venturi (as in US. Patent No. 2,367,507). The air flow signals, thus derived, vary the position of a mechanical control valve in the fuel line, or control the differential fuel pressure across a fuel flow orifice. Ineither event, the fuel is not injected directly into the intake valves of the engine, but is supplied to the moving air stream. As a result, the actual distribution of fuel to the various cylinders tends to be quite irregular, and, particularly under partial load conditions, it becomes substantially impossible to achieve an optimum fuel-air ratio.

Arrangements of this same general type have also been suggested for use in conjunction with fuel injection systems where the quantity of fuel being controlled is supplied directly to the several cylinders of the engine. Where stationary venturi arrangements are employed, it has been found in practice that the air flow signal, derived for controlling the fuel flow, tends to be relatively weak, and the actual control of the mixture ratio therefore 3,409,276 Patented Nov. 5 1968 tends to be inaccurate. Efforts have been made to correct this by using movable venturi arrangements in such fuel injection systems; and while the control is thereby considerably strengthened, above the pressure range of 0.1 to 1 ata. (1.4 to 14 p.s.i.) the signal is no longer proportional to the weight of air introduced into the engine, wherefore the signal derived again does not produce an accurate mixture ratio.

In an effort to correct this further shortcoming, additional controls have been suggested for use in conjunction with the injection pump, for further modifying the quantity of injected fuel as a function of one or more parameters bearing on the weight of air being introduced. However, the resultant structure tends to become quite expensive, and extremely complicated in structure rendering the overall system more susceptible to malfunction.

The primary object of the present invention resides in the provision of a direct fuel injection control apparatus which is simpler and more robust in construction than anything suggested heretofore, but which results in a highly accurate fuel-air ratio control of the mixture sup- .plied to the several cylinders of the engine. In this respect, the present invention is particularly concerned with a control duct arrangement operative to derive a non-linear differential air pressure signal of the type capable of being achieved heretofore only through the use of complex auxiliary control assemblages employing valves, linkages, bellows, centrifugal regulators, etc. This improved control duct arrangement operates to control a differential air pressure diaphragm which, in turn, is linked to a differential fuel pressure diaphragm operating to control the weight of fuel injected into the engine cylinders as an accurate function of the weight of air supplied to the engine, and without the need of the auxiliary control assemblages considered necessary heretofore.

Summary of the invention In providing for the foregoing objects and advantages, the present invention employs a control duct arrangement which bypasses the throttle controlled air flow passage of the engine, and which directly produces a non-linear differential air pressure control signal accurately related to the weight of air being supplied to the engine. The control duct arrangement includes an elongated duct portion of generally uniform crosssectional area provided with an inlet diffuser section of tapered configuration. The largest cross-sectional area portion of said inlet diffuser communicates with the air flow passage of the engine at a position upstream of the throttle, thereby to produce a fiow of air'in the control duct. One of the pressures used to control the differential air pressure diaphragm is derived from a point adjacent the largest area portion of the inlet diffuser. The inlet diffuser tapers into the aforementioned elongated control duct section of substantially uniform cross-sectional area; and the second pressure utilized to operate the air pressure differential diaphragm is tapped, as a dynamic pressure, from this elongated uniform cross-sectional area portion of the control duct.

The control duct communicates with a further duct portion intersecting the control duct at substantially right angles, and said further duct portion merges into an outlet diffuser Which is tapered along an axis extending at substantially right angles to the direction of elongation of the uniform cross-sectional area duct portion. The largest area portion of the tapered outlet diffuser communicates with the air flow passage at a position downstream of the throttle. The right-angle relationship between said further duct portion and said control duct causes a dynamic adjustment to occur in the pressure being tapped from the control duct due to percussion losses at the point of deflectionbetwcen the control duct and further duct, portion, and due also to the tendency for some air compression to occur at said point of deflection. As a result, the differential air pressure signal actually derived is nonlinear and corresponds to the type of signal which has been obtainable heretofore only by apparatuses employing complex auxiliary control devices.

The system of the present invention further lends itself to adjustments in fuel-air ratio by means of a valve element associated with the inlet diffuser, operative to control the profile of the inlet diffuser. The inlet diffuser profile can be varied manually, or as a function of one or more parameters such as engine speed, engine temperature, air temperatuie, and/or atmospheric pressure, as monitored by appropriate sensors.

Brief description of the drawings FIGURE 1 is a cross-sectional diagrammatic view of a control mechanism constructed in accordance with the present invention; and

FIGURE 2 is a graphical representation of the functional relationship between the pressure drop across the throttle, and the differential pressure control signals derived by the mechanism of the present invention.

Description of the preferred embodiment The control mechanism of the present invention comprises a casing having a fuel inlet 11 coupled to an appropriate fuel pump (not shown), and a fuel outlet 12 which may be coupled in known manner to calibrated injector nozzles (not shown) adapted to distribute fuel directly to the various cylinders of an engine. The quantity of fuel supplied to outlet 12 varies as a function of the size, and differential pressure across, a fuel flow orifice 13. The size of orifice 13 is controlled by a needle valve 14 which is in turn linked by linkage 15 to the main air flow throttle 16 of the mechanism. As a result, the specific fuel flow aperture 13-14 varies in size in correspondence with the specific effective air flow aperture provided by throttle 16.

The differential pressure across orifice 13 is controlled by a further valve 17 which is in turn coupled via rod 18 to a differential fuel pressure diaphragm 19. Diaphragm 19 is, in turn, linked by a rod 21 to an air flow diaphragm 20. By this arrangement, the actual position of fuel valve 17 varies as a joint function of the differential fuel pres sure across fuel diaphragm 19, and the differential air pressures across air flow diaphragm 20; and variations in the differential air pressure across diaphragm 20 effect related variations in the differential fuel pressure across diaphragm 19 and across orifice 13.

The improvement of the present invention relates particularly to a novel arrangement for deriving the differential air pressures which are imposed on diaphragm 20. In accordance with the present invention, air throttle 16 is associated with an elongated bypass duct 21 of generally uniform cross-sectional area. The inlet end of duct 21 is associated with a tapered inlet diffuser 22 the largest area portion of which communicates with the air flow passage 23 at a position upstream of throttle 16. A portion of the air entering passage 23 is thus directed, via enlarged diffuser 22, into bypass duct 21. The primary pressure in the system P appears upsteam of throttle 16, and is imposed on the lower side of diaphragm 20 by means of a duct 24 which communicates with the air flow passage 23 at a position adjacent the largest area portion of inlet diffuser 22.

Control duct 21 is further provided, at its other end, with an outlet diffuser 25. Outlet diffuser 25 is tapered along an axis extending at right angles to the elongated duct zone 21, and the largest area portion of the outlet diffuser communicates with the air flow passage 23 at a position downstream of throttle 16. Outlet diffuser 25 tapers into a duct portion 25a which intersects control duct 21 at substantially right angles to the direction of 4 elongation of said controlldu'ctZl. ApressureP rived via a duct 26 communicating with control'duct21 at a position displaced from the intersection"ofcontrol duct 21 and duct portion 25a; and said pressure P f'is imposed on the upper side of diaphragm 20. Y I

" By the arrangement thus described,"a dynamic adjustment in pressure P occurs with increasinggainflo'w through air flow passage 23. More particularlyfcurvefu' of FIGURE 2 represents the variations in differential pressure across throttle 16 with increases in the volume of incoming air. The differential pressures acr'oss'dia phragm, 20 (P -P do not follow curve a,v howevef, but vary in accordance with curve b ofIFIGU RE 2. An ity crease in the differential pressure across throttle1116 ausjes the differential pressure across diaphragm 20 tofals'o increase, but the differential pressureacross diaphragm increases at a decreasing rate until said differentialpr '1 sure reaches a critical value. Upon reaching 'this critical value, the differential pressure across diaphragm 20 re; mains constant even though vthere may' be furtherfincreases in the differential pressure across throttle 1 6 The non-linear characteristics of curveb is believed tojresult from pressure adjustments in control duct 21 due toji'ncreases in the losses which occur at the point of deflecf tion between control duct 21 and ductportion 25a with increases in speed and expansion of the gas flowing in duct 21, and is believed also to result fromfiompressibilr ity effects at said point of deflection. 7,

Since the quantity of fuel flowing to outlet 12 .varies as a function of the size of orifice 13 and the pressure across said orifice 13, the actualweight of fuel. supplied to outlet 12 varies with variations in the position brats. phragm 19. The position of diaphragm 19 dependsupon a balancing ofthe forces across diaphragm 19 and across. diaphragm 20. Since the pneumatic control pressure across diaphragm 20 is proportional to the square of the weight of incoming air, and since the differential pressure across diaphragm 19 is in turn proportionalto the square of the rate of fuel flow, a precise mixture ratio of air weight rate of flow to fuel Weight rate of flow is achieved.

The mixture ratio thus achieved by the arrangement of FIGURE 1 is adjusted statically with variations in the position of throttle 16, which cause related variations in the position of needle valve 14. The mixture ratio can also be adjusted dynamically by changing the profile of inlet diffuser 22 through variations in position of a further valve element 27. Valve element 27 can be varied in position by various mechanisms, and can be moved, for example, as a function of engine speed to adjust the fuel-air ratio even though throttle 16 is not being moved. Similarly, the mixture ratio can be adjusted as a function of air temperature (by means of a bimetallic temperature sensor coupled to valve element 27), or as a function of any other desired parameter such as engine temperature, or atmospheric pressure.

The distribution of fuel to the various cylinders is obtained in the usual manner by use of calibrated nozzles. Under increasing engine load (corresponding to opening of the throttle 16) the apparatus operates to produce a decreasing differential pressure. This characteristic is advantageously used to temporarily cause more fuel to be injected than is required for a normal mixture ratio when the throttle is opened rapidly, corresponding to acceleration of the engine, by proportioning the passage 26, which transmits pressure P to the upper side of diaphragm 20, in such a way that rises in pressure adja cent the upper side of diaphragm 20 are retarded. Acceleration pumps, of the types conventionally used with carburetors, can therefore be omitted.

I claim:

1. In a fuel injection apparatus of the type comprising a differential air pressure device, a differential fuel pressure device, and fuel metering means under the joint control of said fuel pressure and air pressure differential devices, the improvement which comprises intake duct means defining an air flow passage having a variable position air throttle therein, a control duct, one end of said control duct opening into said intake duct means at a position upstream of said throttle and the other end of said control duct opening into said intake duct means at a position downstream of said throttle whereby a portion of the air flowing through said intake duct means is bypassed to flow around said throttle via said control duct, and a pair of pressure difierential lines extending respectively between spaced points on said control duct and said differential air pressure device.

2. The fuel injection apparatus of claim 1 wherein said control duct is elongated in configuration and is provided with inlet and outlet diffusers at its opposing ends, said inlet diffuser comprising a flared portion of said duct having a relatively large cross-sectional area at one end thereof communicating with said air flow passage at a position upstream of said throttle and decreasing in cross-sectional area toward said elongated control duct, said outlet diffuser having a portion of relatively large cross-sectional area communicating with said air flow passage at a position downstream of said throttle and decreasing in cross-sectional area between said downstream position and said control duct.

3. The fuel injection apparatus of claim 2 wherein said outlet diffuser decreases in cross-sectional area along an axis intersecting said elongated control duct at an angle, one of said pair of pressure differential lines being coupled to said air flow passage at a position adjacent the relatively large cross-sectional area end of said inlet diffuser, and the other of said pressure differential lines communicating with said control duct at a position located between said inlet diffuser and the junction between said outlet diffuser and said elongated control duct.

4. The fuel injection apparatus of claim 3 wherein said elongated control duct is of substantially uniform cross-sectional area between said inlet and outlet diffusers.

5. The fuel injection apparatus of claim 3 wherein said outlet diffuser tapers into a duct portion of substantially uniform cross-sectional area, said duct portion extending in a direction intersecting said elongated control duct at substantially right angles.

6. The apparatus of claim 2 including means for adjusting the profile of said inlet diffuser.

7. The apparatus of claim 6 wherein said adjusting means includes a variable position valve element disposed adjacent the relatively large cross-sectional area end of said inlet diifuser.

8. The apparatus of claim 1 including means for adjusting the cross-sectional profile of said control duct.

References Cited UNITED STATES PATENTS 2,160,067 5/1939 Gistucci 261-69 X 2,341,257 2/1944 Wunsch 26l6'9 X 2,500,088 3/1950 Mock 261-69 X HARRY B. THORNTON, Primary Examiner.

T. R. MILES, Assistant Examiner. 

